1. Field of the Invention
The invention relates generally to information systems, and in particular, to networked information systems wherein information objects supplied from an information service to a user agent may include references to other information objects.
2. Description of the Related Art
The explosive growth of internet-based information services, particularly World-Wide Web (WWW) based services, and the increasingly ubiquitous nature of browser technology have created an increased level of demand for network bandwidth. At the same time, typical commerce grade web sites incorporate more and more complex mixes of multimedia content such as images, audio and video, functional code such as applets, and other information objects. Because these information objects are typically served from web servers that are remote from any particular client agent (e.g., a browser), their use contributes to overall network bandwidth requirements. From a browser user's perspective, limited network bandwidth typically manifests itself in delays in rendering web pages or the images, audio and video included therein.
Caching is a technique that is commonly used in information systems to address limited bandwidth between an information source and an information target. In the context of the internet, caching techniques have long been used to improve performance of some information services, notably Domain Name Services (DNS). More recently, caching techniques have been applied to address bandwidth limitations on WWW traffic. For example, network caches are now often integrated with proxy server technology to service requests for HyperText Markup Language (HTML) content. By using such a proxy cache, a request for an HTML object ultimately served by a remote web server may be satisfied with a cached version of the HTML object stored closer to the requesting web browser. Examples of proxy caches include the CERN httpd (available in source from at http://www.w3.org/Daemon) configured as a proxy server with caching enabled, see generally, Luotonen & Altis, World-Wide Web Proxies, April 1994 (available at http://www.w3.org/History/1 994/WWW/Proxies).
Web pages are typically obtained by a web browser by requesting an HTML document from a web server (or from an intervening proxy server) in accordance with a Uniform Resource Locator (URL). In response, the web server (or the proxy server) supplies a corresponding HTML document. Web pages encoded as HTML documents frequently include references to objects such as images, applets and other HTML documents. Sometimes these references are associated with a hyperlink. References are typically encoded in the HTML document as Uniform Resource Locator (URL) references. In the course of rendering an HTML document, the receiving web browser requests these included images, applets and other HTML documents by making additional requests for the objects corresponding to these
Uniform Resource Locator (URL) references. In response, corresponding web servers (or the proxy server) supply(ies) the referenced objects.
Even if each referenced object is cached by the proxy server, to render a given web page, the browser must parse the requested and received HTML document to extract the included URL references, individually request the objects corresponding to the included references, receive each of the requested objects, and finally render each of the received objects. Often, there are significant performance delays for the browser user due to the back-and-forth communication between the browser and the server or servers providing the HTML document and included objects.